Firstly, a conventional loudspeaker is described with reference to FIG. 19 showing a top view of a conventional long shaped loudspeaker (especially, a loudspeaker with a large length to width ratio in shape, which is hereafter generally recited as a “slim loudspeaker”), and FIG. 20 showing a two-directional sectional view in lengthwise and widthwise directions of the slim loudspeaker.
Magnetic circuit 6 shown in FIG. 20 comprises lower plate 6a, ring-shaped magnet 6b, and upper plate 6c. Frame 5 is bonded to the magnetic circuit 6. An outer peripheral portion of diaphragm 2 is bonded to the frame 5 via edge 1, and an inner peripheral portion thereof is bonded to voice coil 3 inserted in magnetic gap 6d of the magnetic circuit 6.
An outer peripheral portion of damper 4 is bonded to the frame 5, and an inner peripheral portion is bonded to the voice coil 3 to support the voice coil 3.
As the edge 1 used in such a loudspeaker, there are a “fixed edge” which is formed of an extended portion of a diaphragm material, and a “Free edge” using other material. Structurally, the former is formed in one-piece structure using a same paper material as the diaphragm by extending a portion thereof, and a plurality of corrugations that are similar to the outer peripheral portion of the diaphragm are formed to provide compliance. The latter is generally made of urethane foam, foamed rubber or like materials, which is formed into a sheet and thermally formed into a predetermined shape such as a corrugation edge and a roll edge.
The edge 1 is required to have two functions, which are:
(1) to support the diaphragm 2 so as not to induce troubles in terms of vibration, and also to reproduce sound free from non-linear distortion; and
(2) to suppress an anti-resonance and a partial resonance of the diaphragm 2, including the edge 1, by absorbing vibration energy of the diaphragm 2 so that reproduced sound quality is not badly affected by a generation of dip on “output sound pressure level vs. frequency” characteristics of the loudspeaker.
To address this above requirement, the edge 1 is required to have appropriate stiffness and to be excellent in terms of mechanical internal losses and linearity relative to displacement of the diaphragm 2 due to a driving force. In order to satisfy these requirements, a material of the edge 1, a sectional shape along a radial direction thereof, and a weight and weight distribution thereof have been studied.
Regarding a shape and structure of the edge 1, which supports the outer peripheral portion of diaphragm 2, corresponding to various shapes of loudspeakers such as the slim loudspeaker mentioned above, there are problems to be solved. That is, results of studies are not satisfactory with regard to “sectional shape, weight and weight distribution, and stiffness” in relation to “mechanical internal losses and linearity of displacement relative to driving force.”
In order to address the above problems of a conventional edge, the present invention provides a loudspeaker having an edge improved in terms of sectional shape, weight and weight distribution and stiffness distribution, taking into account a relationship of displacement linearity of the edge itself and a mechanical impedance of a diaphragm. The loudspeaker of the present invention is excellent in terms of acoustic characteristics such as frequency characteristics, transient characteristics, and distortion characteristics.